1. Field of the Invention
This invention relates to a rotatable grip actuating system for use with a Bowden tube (cable within a tube) type motion translation system. More particularly, it relates to a detent spring for use in a rotatable grip actuating system designed for operating a derailleur gear shifting system on a bicycle.
2. Description of Related Art Including Information Disclosed Under 37 CFR .sctn.1.97 & 1.98
One type of shift actuator that is conveniently rotatably mounted on a handlebar and positioned so as not the require the rider to remove a hand for the customary handlebar grip to operate the actuator is disclosed in U.S. Pat. No. 5,102,372 issued Apr. 7, 1992 to three of the co-inventors of this application and assigned to the assignee of this application. Copending application Ser. No. 08/207,249, filed Mar. 7, 1994, now U.S. Pat. No. 5,476,019 of which this application is a Continuation-In-Part, and which is also assigned to the Assignee of this application, sets for an improvement in the actuating system set forth in U.S. Pat. No. 5,102,372. The improvement set forth in the co-pending application is in part directed to maximizing the mechanical advantage of a rotatable grip actuating system by minimizing the radius at which the cable is pulled. For the purpose of providing a full teaching of the construction and operating requirements of bicycle derailleur-type shifting systems, and particularly ones operated by a rotatable grip actuating system, the above-mentioned patent and co-pending patent application are incorporated herein by reference.
The rotatable grip actuating systems set forth in the above-cited patent and co-pending patent application, each have two principal components which are rotatable with respect to each other. Notches are provided in facing circumferential surfaces of the two principal components. These notches cooperate with a spring to establish predetermined positions of the two principal components with respect to each other. The predetermined positions correspond to predetermined shifted positions of the derailleur chain.
As shown in the patent, and FIGS. 1 and 2 of this application, the spring has in the past been formed as a plastic member. Referring to FIG. 1, the prior art plastic spring 200 has feet 202 and 204 located in a spring cavity 206, and an indexing projection 208 engaged in a detent notch 210 in the detent notch circle 212. The detent notches 210 have a differential between the angle on the cable release side of the detent notch and on the cable pull side. This differential in angles was provided to substantially balance out the torque required to rotate the grip out of a detent notch, since the cable tension provided by the derailleur mechanism naturally pulls the rotational grip in the direction of cable release.
As can be seen in FIG. 1, there are space limitations for accomplishing the detent action. The curvature of the handlebar and the curvature of the detent notch circle leaves a predetermined narrow arcuate space. Thus, it was found necessary to use a leaf spring in that space to provide the detent action, and a plastic leaf spring was first chosen. It has been found that the plastic spring 200, when left with the indexing projection or detent 208 between the notches, tends to deform plastically because of cold flow of the plastic caused by the continuous stress. That is, when the detent 208 is positioned between notches, it is pushed toward the center of the grip, with the leaf portions 214 being flattened. This deformation can result in the loss of the preload contact force between the detents 208 and the notches 210. The torque required to release a detent 208 is a function of the spring preload, contact angles and the stiffness of the leaf portions 214 of the plastic spring. If the preload force of the spring is significantly reduced, the release torque is also significantly reduced.
In another embodiment of the prior art as shown in FIG. 2, the leaf portions 214 of the plastic spring 200 are supported, when the detent 208 is in a notch 210, by a pair of feet 216 which engage a correspondingly located pair of projections 218 in the cavity 206. This embodiment was intended to maintain the preload force on the spring when the detent 208 was in a notch 210.